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PROF. ABBES PAPER. 211 


PROF. ABBE’S PAPER ON THE RELATION OF 
APERTURE AND POWER IN THE MICROSCOPE. 
E announced in the last number our intention to give an 
abstract of Prof. Abbe’s paper, but finding it could not be 
usefully abstracted, it is presented to our readers zz extenso. 
We do not agree with some of the conclusions, especially those 
in which it is stated that two objectives of the same power but dif- 
ferent apertures are necessary; nor with the statement that wide 
apertures by being cut down produce bad objectives; but as the 
proof of the pudding is in the eating thereof, we intend to present 
our readers next month with a series of photographs to prove the 
position we have taken up, and to show that low power objectives 
of wide aperture (up to a certain limit) are not only necessary, 
but are the best appliances with which to conduct microscopical 
research. 
With the higher powers we do not differ much from Prof. Abbe’s 
views, and any one who has studied bacteria under an eighth of 
110° air-angle, and again under a fifteenth of 110° water-angle, will 
be ready to admit the superiority of the pictures yielded by the 
latter. 
What we shall argue for will be two-inch objectives of 20° air- 
angle, one-inch of 35° and the half-inch of 66°. Something may 
be said regarding the quarter-inch and eighths, but the lower 
powers will be used to demonstrate that the position we have taken 
up is a correct one. 
In this connection we have no wish to discourage the purchase 
of low-angle lenses by amateurs, but we hold that every instrument 
used in scientific research should be the best of its kind, and every 
device not calculated to produce a correct picture of an object— 
to tell the truth, the zw/o/e truth, and nothing but the truth— 
should be discarded, except when used for purposes of amusement, 
or for observations by no means critical. 
We think Prof, Abbe has been exceedingly unfortunate in his 
selection of a simile when he states, “‘ To recommend the applica- 
tion of wide-angled objectives for every branch of microscopy, as 
has been, in fact, done by excited wide-aperturists, is no more to be 
supported than it would be to recommend the use of a magnifier 
to a painter for inspecting the tree which he proposes to delineate.” 
We may be singular in our tastes, but we certainly prefer to see 
a tree delineated with rugged bark, enlivened with natural patches 
of orange-yellow and olive-green, betokening the presence of 
lichens, and the dark-green of mosses, tHe details painted in ; in- 
stead of a broad wash of colour, putting one more in mind of a 
